1. Field of the Invention.
This invention relates to plugs for use in wellbores and particularly to plugs for use in operations in cased wellbores which require the breaking off of frangible breakaway members.
2. Prior Art.
Plugs are used for various purposes in wellbores and in wellbore operations. In cementing operations, plugs with flexible wipers are used to act as a barrier between cement and displacement fluid to prevent fluid/cement intermingling; to wipe off fluid such as drilling mud or cement from the interior casing wall; to provide means for indicating when cement has been displaced from within the casing; and to break off frangible breakaway members such as breakaway plugs which protrude into the casing.
The available plugs have proven to be unsatisfactory, particularly plugs which have to pass restrictions such as stage cementing tools. The flexible wipers of the prior art plugs are not rigid enough to insure that breakaway plugs are broken. A very serious problem created by the prior art plugs is the forward migration of broken off plugs, plug pieces, or other items which become lodged inside check valves, landing baffles or other operative members in the wellbore.